1. Field of the Invention
This invention relates to detecting an abnormality in determining the quantity of intake air being supplied to an internal combustion engine.
2. Prior Art
U.S. Pat. No. 4,483,229, discloses a method for detecting an abnormal output value of a sensor and for substituting a previously stored "error free" value in place of the detected erroneous value. There is no teaching of calculated redundant airflow values which are compared with one another to determine the possible and correct measurement. In particular, the patent teaches determining the presence of specific failures where the sensor outputs a constant value equal to a specific not expected value for some length of time. For example, for a manifold pressure sensor, this type of failure will result from the sensor being physically disconnected, the vacuum connection to the intake manifold is obstructed or there is a rather gross failure of the sensor itself.
Other diagnostic systems with various inputs are also known. A first input to the diagnostic system can be from the air meter. This meter measures the mass of air flowing into the engine's intake manifold. An alternate system is a calculation based upon engine speed (rpm), intake manifold pressure (MAP), and some other factors. Airflow is also inferred from measured throttle position (TP), rpm and density corrections (barometric pressure (BP), and inlet air temperature (ACT). These measurements of airflow are currently used. It is also known to perform rationality checks based on relations between air mass and TP to detect failures. These checks do not, however, indicate which of the two measurements are at fault. These are some of the problems this invention has overcome.